1. Field of the Invention
The present invention relates generally to a tape cassette construction. Specifically, the present invention relates to a tape cassette structure which reliably enables a cam boss of a sub lid of the cassette to return to its original position smoothly even if a cam boss portion thereof enters a concave portion due to misoperation.
2. Description of the Prior Art
Tape cassettes are widely used as a data storage medium in a number of audio, video and data processing applications. Conventional, 8 mm video cassettes utilize a closed cassette format having a housing construction utilizing a lid and a sub lid. A cam boss portion of the sub lid is guided by a cam groove provided on each side of an open portion of the cassette housing, which portion is opened and closed according to movement of the lid and the sub lid.
A cassette housing has two tape exit portions at each side of a front of the cassette housing. These tape exit portions are opened and/or closed by movement of the lid. A cam boss portion of the sub lid is guided by a cam groove provided on an inner wall forming the tape exit portion.
Operation of such a conventional cassette structure will be explained hereinbelow with reference to FIGS. 8-11.
FIG. 8 shows an enlarged perspective view of a conventional cam groove portion 101 formed in a shell of a conventional tape cassette (not shown). As may be seen in the drawing, the cam groove portion 101 is located at the front of the cassette housing. A main lid 107 and a sub lid 105 (FIG. 9) being mounted between opposing cam groove portions 101. The cam groove portion 101 includes a cam groove 104, a concave portion 103 and a substantially semicircular tape guide portion 102 is formed on a rear side of the concave portion 103. The concave portion is formed for preventing the surface of the tape guide portion 102 from shrinking and becoming concave during molding of the cassette shell as such shrinkage and concavity of the tape guide portion 102 may prevent the magnetic tape in the cassette from running smoothly and may injure the surface of the magnetic tape.
Referring now to FIG. 9, an enlarged cross-sectional view of a cassette main lid 107, sub lid 105 and the conventional cam groove portion of FIG. 8 is shown.
The main lid is pivotally attached to the cassette housing at a main axis 108 and the sub lid is pivotally attached to the main lid at a sub axis 109. As may be seen, a cam boss 106 is positioned in a lower portion of the cam groove 104 when the tape cassette is in a closed state.
A length of magnetic tape 111 is interposed between the main lid 107 and the sub lid 105. During opening operation, the main lid 107 is rotated in the clockwise direction of FIG. 9 along with the sub lid 105 causing the cam boss 106 to be moved in the upward direction to be extracted from the cam groove 104 thus exposing the magnetic tape 111 for extraction and/or winding operations, as may be seen in FIG. 10.
On the other hand, during closing operation, the above movement is reversed.
It may occur that the sub lid 105 is pushed or dislodged by misoperation of the user such that the cam boss 106 moves over the rib forming the cam groove 104 in the direction of the arrow a of FIG. 9. After moving over the rib, the cam boss 106 enters a concave portion 103. In this state it is difficult to return the cam boss 106 to the cam groove 104.
Thus, it is necessary to provide a tape cassette structure in which smooth, reliable opening and closing of the lid and sub lid portions is assured.